5 as you descend through water columnlose more and more lightreds go first (lower energy)gives a bluish cast to everythingmuch more pronounced locally than in the Caribbeanwe have far more photosynthetic organisms in the waterabsorb the light (red & blue ) for photosynthesis - leaves green

6 Tropical waters are still very PRODUCTIVE bottom of food chain eventsSo- the blue colour & clear water of tropics due to few photosynthetic organisms in tropical watersTropical waters are still very PRODUCTIVEbottom of food chain eventsprimary productionproduction of organic material from inorganic

8 Primary Production trophic pyramids/webs - find plants at the bottomuse SUNLIGHT energy to fix CO2 into organic moleculesPrimary Productionplants consumed by primary consumers etc.less total biomass as you go up the pyramidincrease size of organism as you go up the pyramid

9 eximine coral reefs ecosytem:“how does this flourishing ecosystem survive with so few producers - the plants ” ?clear water, few phytoplankton ???

10 In the reef system primary production is mostly BENTHIC (bottom)Open ocean (or local Maritime), primary production is mostly PELAGIC (water column)

11 Much of the productivity from corals Cnidaria - from the Latin “nettle” – a planthave often been mistaken for plantsattached to a substratedo not wander aboutsame colour as manymarine plantssame branched natureand growth habit

12 were originally classified as plantsby the naturalist John Ray ( )In 1723, Jean Peyssoneldecided they were animals

13 naturalist John Ellisa microscope modified for aquatic workfound the animal polyps on many reef organismsthen considered to be animals for a while - with no plant componentimprovements in microscopy confirmed their animal nature, with polyps filtering out plankton with their tentaclessubsequent studies showed that the reef is composed of many organisms, as well as the Cnidarians

22 so where were the primary producers ??20C - new understanding of trophic pyramids, attention turned to reef productivityvery productive (produce lots of biomass)lots of lifelots of diversityproductivity couldn’t be due just to the calcareous green and red algaeso where were the primary producers ??

23 Extensive examination of atolls (Eniwetak – Marshall Islands)lots of encrusting algae on the surface of corals, but also ...examine corals in more detailtrue nature of the Cnidariansalgae growing inside the cells of the coral polyp

24 These algae - ZOOXANTHELLAE enough algae inside the coral polyp to account for massive primary productiontheir presence explained the plant-like growth habit of the Cnidarian -to increase surface area for light absorptionAlso explained the colours of the corals

25 1950s - Tom & Gene Odumsuggested the coral polyp and the alga were in some sort of mutualistic relationshipthe polyp itself is a miniature ecosytemthe two organisms exchange nutrients and other benefits“Trophic Structure and Productivity of a Windward Coral Reef Community on Eniwetok Atoll”

27 extend tentacles - mostly at nightzooplankton are most plentiful (move up from deeper waters)whole surface of the coral becomes a trap for planktonparalyze preysting with NEMATOCYSTStrap preysticky MUCUS ontentacles

28 tentacles produce WAVE-LIKE action sweeping the mucus and prey into the mouthdown the pharynx (gullet) to the gastrovascular cavity for digestion

30 Tentacles mostly retracted during the dayhelp corals avoid predationprotect from UVCorals also get some nutrients from seawaterdissolved amino acidsglucoseinorganicsnot usually much, except in locally polluted areas

31 Most scleractinian (stony) coralsstructure of the polyps and skeleton of the coral is a simple combinationMost scleractinian (stony) coralscolonies of polypslinked by common gastrovascular system (coenosarc)polyp made up of two cell layersouter epidermis (or ectoderm)inner gastrodermis (endoderm)

34 The corallite is the part of the skeleton deposited by one polypThe skeletal wall around each polyp is called the thecaThe coral structure also includes calcareous plate-like structure known as septa

35 One of the epidermal cell types is the cnidocytecontains organelles called nematocystsdischarge toxic barbed threadscapture zooplankton prey

37 gastroderm cells line the body cavitycapable of phagocytosis (food particles)contain the intracellular algaeextend into tentacleszooxanthellae not in direct contact with the cytoplasm of the coral gastroderm cellzooxanthellae reside inside a vacuolethe symbiosome (animal origin)

38 Much of the food needed by the polyp comes from the SYMBIONTMany corals have different growth forms - can vary with local environment - light, depth etc.Local environment affects distribution of the zooxanthellae